April 07,2024By:Innova OpticsView:208
With the continuous progress of uncooled infrared focal plane, the infrared thermal imaging market has developed rapidly. The technical applications of uncooled infrared thermal imaging products can be summarized into three main directions: visual enhancement, non-contact temperature measurement, and preventive detection.
The uncooled infrared imaging sensor is composed of many MEMS micro-bridge structure pixels arranged repeatedly in two dimensions on the focal plane. Each pixel measures the thermal radiation at a specific incident angle. Its basic principle is as follows:
(1) Infrared radiation is absorbed by the infrared absorbing layer in the pixel, causing temperature changes, which in turn changes the resistance of the amorphous silicon thermistor;
(2) The amorphous silicon thermistor is supported on the silicon substrate through the MEMS insulated micro-bridge, and is connected to the COMS independent circuit produced on the silicon substrate through the support structure;
(3) The CMOS circuit converts the resistance change of the thermistor into a differential current and performs integral amplification. After sampling, the gray value of a single pixel in the infrared thermal image is obtained.
In order to improve the response rate and sensitivity of the detector, the detector pixel microbridge is required to have good thermal insulation. At the same time, in order to ensure the frame rate of infrared imaging, the heat capacity of the pixel must be kept as small as possible to ensure a small enough thermal time constant. , so MEMS pixels are generally designed with a structure as shown in the figure. Slender micro-cantilever beam supports are used to improve the thermal insulation performance. Heat-sensitive materials are made on the bridge deck. The bridge deck is as light and thin as possible to reduce thermal mass. A reflective layer is made on the substrate to form a resonant cavity between the substrate and the bridge deck to improve the infrared absorption efficiency. The pixel micro-bridge is connected to the CMOS readout circuit in the substrate through both ends of the cantilever beam. Therefore, the uncooled infrared focal plane detector is a large array device integrated with CMOS-MEMS.
Uncooled infrared imaging sensors have a wide range of applications in military and commercial fields:
(1) Military field
As shown in the figure, it is used for weapon thermal sighting, portable vision enhancement, vehicle-mounted vision enhancement, remote weapon stations, drones, unmanned ground vehicles, observation and command vehicles, fire control, guidance, etc.
(2) Thermal imaging temperature measurement
It is used for preventive detection, such as detecting abnormal heating areas through infrared thermal imaging cameras on power transmission lines, power generation equipment, mechanical equipment, etc., which can prevent major shutdowns and accidents. In construction, it is used to detect the insulation effect of houses, wall facades, hollows, water seepage, mildew, etc. Other fields include product research and development, electronic manufacturing, medical thermometry, medical testing, process control, etc.
(3) Commercial visual enhancement
Current main applications include fire rescue, security monitoring, vehicle-mounted, ship-mounted infrared vision enhancement, etc. It mainly uses the advantages of infrared imaging, which does not require external light sources, has a strong ability to penetrate smoke, has a long operating distance, and has strong imaging contrast, to effectively supplement human vision.
(4) Consumer electronics
Due to the wide application and extremely high penetration rate of visible light image sensors in consumer electronics such as mobile phones, people have high expectations for the application of infrared imaging in consumer electronics. The wide-scale application of infrared thermal imaging technology in consumer electronics is currently mainly limited by cost and volume. It also makes people look forward to more applications of infrared thermal imaging sensors in the field of consumer electronics.
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